1. Field of the Invention
The present invention relates to a fuel vapor release suppression system for a fuel tank, in which a main tank and a sub tank communicate with each other via a communication passage, and the sub tank and a canister communicate with each other via a charge passage.
2. Description of Related Art
Japanese Patent Publication No. 3659005 discloses an automobile fuel tank arrangement wherein a sub tank is provided separately from a main tank, and is placed in a low temperature environment as compared with the main tank. In this arrangement, fuel vapor is supplied from a gas-phase portion of the main tank, having a higher temperature, to a liquid-phase portion of the sub tank, having a lower temperature, and is liquefied therein. In addition, the liquefied fuel is returned to the main tank, thereby reducing the load on a canister that is charged with fuel vapor and lowering the concentration of fuel vapor that is purged from the canister into an intake passage of an engine to reduce the influence on combustion of the engine.
In this conventional arrangement, fuel vapor generated in the main tank can be liquefied in the sub tank when the temperature of the sub tank is lower than that of the main tank, but the fuel vapor cannot be liquefied when the temperature of the sub tank is higher than that of the main tank. Therefore, in order to enable constant fuel vapor liquefaction, the temperature of the sub tank is required to be lowered by using a cooling device, leading to a problem that the power consumed by the cooling system imposes a burden on the vehicle battery.